So, the reason I told you that you might have some trouble with your equipment theme, is what you are seeing here: the vast majority of equipment is terrible.
Stoneforge mystic is not a great card: batterskull, jitte, and swords of X and Y are great cards, and stoneforge is great at finding them. Once you strip those away, this is what you are left with for best generic equipment options:
Maybe
loxodon warhammer and
behemoth sledge. Everything else is very niche. The equipment that I've ran that I've enjoyed over here has been:
Piston sledge is a great card if you are running an artifact theme with sac. targets and metalcraft creatures (note there are only a handful of cubeable metalcraft cards). Trepanation blade is not a good card, however it is a very entertaining card. Bonehoard is very strong, but wants a slower enviornment.
I also think these cards are solid role players, though nothing really strong.
Husk is good anti-edict tech, adds to artifact count, and can grow creatures just enough to outsize an opposing creature or move it out of burn range. Mortarpod is a nice pinger and sac. outlet.
This card has also been on my radar for a while, though its never made it into a cube.
You probably are best off just picking whatever niche equipment fits your cube's design the most.